1. Field of the Invention
The present invention relates to a process for the preparation of a polyimide film which is improved in adhesiveness. More particularly, the invention relates to a process for the preparation of a polyimide film which is improved in adhesiveness to a metal foil such as a copper foil in the case of bonding the polyimide film to a metal foil through an epoxy type heat-resistant adhesive.
2. Description of Prior Art
It is generally known to prepare a high heat-resistant polyimide film using an aromatic polymer composition which comprises an aromatic polyamic acid produced from an aromatic tetracarboxylic acid component mainly containing a biphenyltetracarboxylic acid or a dianhydride thereof and an aromatic diamine component mainly containing a phenylene diamine, dissolved in an organic solvent by utilizing a solution casting method, etc., as described for instance in Japanese Patent Publication No. 60(1985)-42817.
The polyimide film of biphenyltetracarboxylic acid type prepared by the above-described method is very excellent in various properties such as heat resistance, mechanical strength and dimensional stability, so that the film is suitably employed as a support of a flexible circuit-printed copperplated board (FPC board). However, in the case of combining the polyimide film with a metal foil such as a copper foil by means of a heat-resistant epoxy resin adhesive, satisfactory bonding strength between the polyimide film and the metal foil is hardly obtained. Therefore, this problem has been expected to be solved.
For example, an IBM Report describes an result of an experiment of coating 0.1% aqueous solution of .gamma.-aminopropyl-trimethoxysilane on a surface of a solid film of pyromellitic acid polyimide prepolymer and an organic solvent (Polymer Science Technology (USA) 29, 517-523, 1984).